Hydrogen gas is used in the manufacture of many products including metals, hydrotreating and hydrocracking in refineries, commercial catalytic hydrogenation for high volume chemicals, edible fats and oils processing, and in semiconductors and microelectronics industrial processes. Hydrogen gas is also an important fuel source for many energy conversion devices. For example, fuel cells use purified hydrogen and an oxidant to produce an electrical potential. Thus, hydrogen gas is a critical component for the production of high-grade chemicals and clean-burning fuels, and is the cleanest, highest energy content fuel on a weight basis. However, because hydrogen is a very explosive gas, its use has been limited by the need for supplying it in high-pressure cylinders.
There are numerous industrial methods for the generation of hydrogen gas including electrolysis of water (U.S. Pat. No. 5,037,518), reaction of a metal with an acid, reaction of certain metals with a strongly alkaline compound, reaction of calcium hydride with water (U.S. Pat. No. 5,833,934), steam reforming of methyl alcohol or methane in natural gas (U.S. Pat. Nos. 4,454,207 and 4,642,272), releasing of hydrogen gas from a hydrogen-loaded hydrogen-absorbing metal or alloy (U.S. Pat. No. 6,596,055), and so on.
One of the current limitations in developing fuel cell technology is the lack of an efficient, controllable, and cost-effective method for producing hydrogen (H2) on an ‘as-needed’ basis for reaction in the fuel cell. For example, current chemical hydride methods of generating H2 have the drawback that once H2 production begins, the reaction cannot be stopped. Thus, H2 continues to be produced and either must be used by the fuel cell, stored as a gas, or wasted due to release. Alternatively, H2 for a fuel cell can be stored as liquid hydrogen. However, this requires specialized equipment to safely store the liquid H2 under the necessary temperature and pressure conditions. Additional shortcomings of current methods include low yield from the hydrogen producing reactions, severe processing conditions such as high reaction temperatures, consumption of a large quantity of energy, and high operating costs. Thus, efficient and cost-effective methods for producing H2 on demand are needed, preferably where hydrogen is produced from a hydrocarbon fuel source.
Hydrogen has been generated from hydrocarbon fuel sources in a process called steam reforming where steam and a hydrocarbon are reacted in the presence of a catalyst. Examples of suitable hydrocarbons are alcohols, such as methanol or ethanol, and alkanes such as methane, propane, gasoline or kerosene. Steam reforming requires an elevated operating temperature of between 250° C. and 900° C., and produces primarily hydrogen and carbon dioxide, with lesser quantities of carbon monoxide also being formed. Efficient operation of the fuel processor requires careful indexing and control of the ratio of water (steam) to carbon-containing feedstock. Trace quantities of unreacted reactants and trace quantities of byproducts also can result from steam reforming. Therefore, a subsequent purification process to remove the impurities is normally employed. The process thus requires high capital costs. In addition, due to the size of the reactor, steam reforming is not suitable for the purpose of hydrogen supply to fuel cells which must naturally be very compact in size and light in weight. Thus, steam reforming is only economically viable for large, commercial scale production of hydrogen gas.
Thus, there is a need for methods of producing of hydrogen gas that are efficient and cost-effective. Preferably the methods allow for the production of hydrogen on an as-needed basis with little or no impurities being formed, requires low capital costs, and produces hydrogen gas in a process that is environmentally friendly.